Fingerprinting mercury pollution

Mercury is a neurotoxin. The Environmental Protection Agency says mercury can be especially harmful for babies and kids. Mercury can affect their developing brains and harm their memory, attention, language and motor skills.

Mercury is naturally-occurring. Volcanoes emit mercury and so do hot springs, like the ones in Yellowstone National Park.

But the EPA points out... the largest manmade source of mercury emissions in the U.S. comes from coal-burning power plants.

Joel Blum is a professor of Earth and Environmental Sciences at the University of Michigan. Blum says when power plants burn coal, mercury is emitted as a gas.

“In order to become toxic, it has to be transformed into a particular form known as methylmercury which is something that happens in the environment.”

So... mercury falls from the atmosphere, and is converted to methylmercury in the water. That toxic form builds up in fish... and it can build up in us when we eat fish.

But for years... there’s been a big debate about where that mercury goes when it’s released from a power plant smokestack.

“How much is deposited nearby, close to the plant, and how much goes into what we call global pool of mercury - basically goes into the atmosphere and stays there for a long period of time and mixes with mercury from other sources.”

Joel Blum and his colleagues have started to crack that puzzle with some careful detective work. They were able to track mercury emissions from a power plant in Florida... and they found that a high proportion of the mercury ended up nearby.

They did this by looking at chemical fingerprints.

“The element mercury has seven different forms that have slightly different masses.”

So – they can measure the ratio of these mercury isotopes and look at very subtle differences.

“And that can be used to tell different batches of mercury apart from one another.”

The team took the fingerprint of mercury in coal from the regions in Kentucky and West Virginia that supply the Florida power plant. And they measured rainfall at sites near the plant... and sites far away from the plant... for a month. It turned out the mercury fingerprint in those rainfall samples near the plant was very different from the mercury coming from other sources from across the Gulf of Mexico.

“So our study basically showed that a large portion of the mercury is being deposited locally from a particular power plant which strengthens the argument that we should be regulating mercury emissions from our own power plants in the United States.”

In Michigan, utility companies have been installing mercury control systems to meet state regulations.

The mercury fingerprinting method has been ten years in the making. But Joel Blum makes a point of saying that this is a very new technique... and there are many questions they still need to answer. For one thing... they still have to get mercury samples from the top of smokestacks.

Laura Sherman is a PhD candidate who’s been working on the project. She says someone would have to go up near the top of the smokestack to get mercury samples.

“They basically sit up there pulling air through little tubes with gold beads in them. All the mercury in the stack will stick to those gold beads, and we can analyze it later, so that’s something we would like to do.”

And she says right now, they’ve only looked at mercury fingerprints from this one power plant in Florida, so they don’t know yet what they’ll find at other plants.

The study is published in the journal Environmental Science & Technology.